DI Boxes - Active or Passive?

[allanr]

I'd always assumed ACTIVE DI's would be the automatic first choice because of their high input Z, and that PASSIVE DI's were the poor relation (not such high input Z, possible poorer freq response).

 

I realise now that passive DI's (by nature of their transformer design) also provide electrical isolation of input/output which may be important in certain applications. However they also attenuate by typically 20db (for 10:1 transformer ratio) hence require connection to the mixer mic-inputs.

 

For keyboards, laptops and other mains equipment which don't need high impedance matching, but do require isolation and balancing, could a simpler interface be used e.g. Orchid 1:1 Transformer and possibly connect to the mixer line-inputs?

 

 

So in summary, are the likes of the BSS AR-133, KT-DN100 (and Behringer DI100) preferred/useful because they are both active AND provide transformer isolation, hence good all-rounders?

 

 

Comments please, but go easy as this is my first post.

[paulears]

I actually think the isolation box does seem to have been missed - many modern mixer premaps are quite happy with a huge range of input levels, so the 'standard' procedure of dropping line level down to mic level and then adding extra gain to get it up again does seem a rather odd 'solution' to a non-existent problem. In most cases all that's needed is something to convert a signal to balanced, with an appropriate impedance to go down the line, and to not load the input source - and a transformer seems an ideal solution. I have got an ancient one somewhere, but with very high quality on stage digital preamps now being fairly common - perhaps a transformer (or electronic) solution would be better. The real issue being the level change?

[Paul O]

I have a couple of these as general all-round balanced to/from unbalanced, isolation & ground loop elimination interfaces. They are passive transformer-isolation boxes with a wide variety of connectors in and out & solve all sorts of connection issues.

[GaryNattrass]

As a mainly broadcast OP all of my interface and DI boxes are transformer balanced passive and I find those ART ones excellent, most of the AV companies I have worked with tend not to have such boxes so it is essential to be able to isolate and remove any hum problems.

 

 

[john deans]

I have always considered that a DI box should include a transformer so there can be ground isolation between the source and PA. At the risk of repeating myself. I have mainly used the EMO passive boxes as they are built like the proverbial brick outhouse recently adding some BSS 133 to my stock. I am tying to persuade one of my friends to let my pull one of his studiospares boxes apart as from the out side they seem remarkably like the BSS133

[Oldradiohand]

I've always thought of them as being as important for isolation (screened transformer with NO earth lift switch, in addition to screened mic splitters) as for balancing. Having seen the difference in "earth" between stage and OB trucks on occasion it's a bit of a lifesaver. Optical stageboxes are definitely the way to go - if you can afford it.

[dbuckley]

Transformers are the enemy of clean audio, and thus theoretically, a DI with a transformer should be used when isolation is required. Otherwise an active DI will give a cleaner signal, especially at the audio extremes. DI boxes with better quality transformers (ie more expensive) are better than cheap transformer coupled DI boxes, again especially at frequency extremes.

 

However, despite me saying that "Transformers are the enemy of clean audio", oft-times one is not interested in clean but "sounds nice", and a transformer can alter the character of the sound to make it "nicer".

[Simon Lewis]

With transformers, isn't there an issue with output impedance? A 1:1 transformer with high enough input Z to present a reasonable load to the source will present a fairly high output Z to the destination. If that is over a long length of cable, it's not ideal...

[TimmyP1955]

Passive DI for active output, active DI for passive output.